Technical Field
This disclosure relates generally to automatic gain control of an analog signal over copper pairs.
Background of the Related Art
The demand for higher frequency transmission of digital and analog data over copper wire continues to increase. Indeed, not only are frequencies increasing, but also the required distance of transmission is increasing as well. Higher frequencies and longer distances create a significant problem for operational amplifier (OPAMP) circuitry designed to receive the data signal at both ends of the copper loop. Physics dictates that signal strength attenuates exponentially with distance. A distance increase of only a few hundred feet can prevent electronic circuitry from working correctly, but product specifications typically require functionality across wide distance variations. An example of this is DSL over copper twisted pairs.
Further, analog signal strength may vary with physical loop conditions such as time, temperature, vibration or moisture. The strength of output of analog sensors, for example, medical sensors, may deteriorate as environmental conditions change; this causes operational amplifier circuits to process signals incorrectly or to constantly self-calibrate.
Ultimately, OPAMP circuitry often has to work with received (input) signals with very wide amplitude and frequency ranges. Very often, there is only very limited power available for the circuit, and the OPAMP needs to also account for transient power surges that will cause noise or data errors. In addition, battery backup or battery-powered circuitry is required in many applications with the above characteristics, but is not always feasible or acceptable due to power requirements.
Under the above conditions, OPAMP circuitry often needs to undergo extensive manual calibration to achieve optimal efficiency. This is not always possible in many situations, such as when the equipment is remotely deployed, when physical access is difficult or impossible, or when it is too costly to get access to the remote equipment or location.
The most widely used solutions in the marketplace today rely on manual calibration or signal processing with the help of a microprocessor or a digital signal processor (DSP). Manual calibration is used and useful where there are limited numbers of variables, adequate physical space on circuit board for jumpers or switches, easy access, low labor cost, stable environment, and documented gain or calibration settings. Unfortunately, this is not the case in many applications, which prevents the use of a manual calibration approach. The more widely-accepted solution is to use digital signal processing (DSP) to compensate for analog signal attenuation and distortion. The DSP-based approach requires converting the analog signal into a digital signal for processing. The standard method is to use an analog-to-digital (A/D) converter with the required number of bits, accuracy, resolution, conversion rate, and cost. Once converted, the digital data also must be processed to calculate the desired action. In many cases, the processing of the data is dependent on the classification of analog signal sent. For example, the processing of an ADSL signal is different than a VDSL2 signal. In addition to the complexity and limitations of signal processing, solutions of this type require significant power and create high current spikes or analog noise.
There remains a need to provide an operational amplifier circuit design that can self-calibrate itself based on a wide range of analog signals in an environment where available power is very limited.